1. Field of the Invention
The present invention relates to an improvement for a numerical control device and an acceleration/deceleration control method for numerical control.
2. Description of the Related Art
Pre-interpolation acceleration/deceleration control and post-interpolation acceleration/deceleration control are known in cases in which tool feed speeds are accelerated or decelerated during transition from the currently executed tool feed step to the subsequent tool feed step on the basis of a tool feed speed specified in advance for each tool feed step by means of tool feed speed values (expressed, for example, in mm/min units), which are given by the amount of movement (tool feed distance) to be made per unit time.
However, in turning, tapping and other type of machining, tool feed rate (for example, mm/rev) for each tool feed step, which is commanded in terms of feed distance per a single rotation of or unit angle of the spindle (hereinafter referred to as an amount of movement per unit angle of the spindle) and rotational speed of the spindle (for example, rev/mm), which substantially represents an angular speed of the spindle, are specified so that the tool is fed according to the rotational speed of the spindle. Consequently, a tool feed speed (for example, in mm/min) expressed as the amount of movement per unit time cannot be provided as part of machining data in a program. As a result, the aforementioned pre-interpolation acceleration/deceleration control based on the tool feed speed expressed as the amount of movement per unit time cannot be applied to turning, tapping, or other types of machining.
In some conventional numerical control devices, the tool feed speed (for example, in mm/min), expressed as the amount of movement per unit time at each tool feed step, is calculated on the basis of the tool feed rate (for example, in mm/rev) at each tool feed step, expressed as the amount of movement per unit rotation angle of the spindle, and on the basis of the current value (for example, in rev/min) of the rotational speed, substantially expressed as the angular speed of the spindle; and this tool feed speed is used for carrying out the post-interpolation acceleration/deceleration control of the tool feed speed at the currently executed tool feed step, which is expressed as the amount of movement per unit time.
However, according to such post-interpolation acceleration/deceleration control, acceleration/deceleration control is carried out after interpolation, thus creating shape errors in the work.